Method of projecting color pictures



June 16, 1942. c T 2,286,930

METHOD OF PROJECTING COLOR PIQTURES Filed July 2, 1940 jive 715E02czZcZmc el 1,44 715.5 QEgZy,

Patented June 16, 1942' Gerald F. Backett, Los Angelea, Calif., minor toTechnicolor Motion Picture Corporation, Hollywood, Calif., a corporationof Maine Application July 2, 1940, Serial No. 843,806

3 Claims. (01. 88-164) In the art of projecting motion pictures innatural colors one of the major problems is to obtain proper balancebetween the three complemental colors used to produce the various huesthroughout the pictures. While the color balance can be controlled inthe process of producing the color film, of course the film cannot bechanged after it is finished. If the projection equipment were the samein all theaters in which the pictures are to be projected the colorbalance could be adjusted to suit the equipment. However, the equipmentin different theaters varies widely, particularly in respect to thecolor of the projection light, and this variation affects the colorbalance. For example, projectors having arc lamps produce a bluish lightwhile projectors equipped with incandescent lamps produce a yellowishlight, and even projectors of the same type produce light of diflerentcolors, respectively, depending upon the voltage and other factorsaffecting the temperature of the light source. If the color balance inthe film is adjusted (in the manufacture of the film) to projectionlight of .one color temperature, the balance will be'wrong forprojection light of another color temperature.

Objects of the present invention are to produce proper color balance inthe pictures reflected from the screen notwithstanding the hue of theprojection light does not correspond to the color balance of the filmpictures, to compensate for the tendency of off-color projection lightto destroy the color balance, to cause each film to produce the samevisual effect in different theaters notwithstanding differences in thecolor temperatures of the projection lights in the different theatersrespectively, and to accomplish the foregoing with maximum efllciencyand minimum expense.

According to the present invention the tendency of the projection lightto destroy the color absorb the ofl-color components of the projectio'nlight; Thus, in each theater, the color of the- 1 screen is correlatedwith the color of the projec tion light in accordance with the colorbalance of the film pictures to be projected, whereby the screenpictures in different theaters have substantially the same color balancenotwithstanding the aforesaid vdiflerences in color of the projectinglight in the different projectors.

The preferred method of determining the proper relationship between thecolors of. the screen and projection light, respectively, is to projectlight from the projector upon an area of the screen, simultaneouslyprojecting light from a standard source upon an adjacent area, andvarying the tone value of the light from the standard source and/or thespectral absorbing qualities of said adjacent area until the two areasapproximately match in tone value.

For the purpose of illustration a typical method of tone determinationis shown in the accombalance of the film pictures is counteracted byabsorbing from the projectio'n light .the color components which tend tomake the color balance of the screen pictures differ from the colorbalance of the film pictures. This absorption of the off-colorcomponents is preferably efiected at the screen, as by painting thescreen the proper shade. For example, if the projection light is l morebluish than the light for which the color balance of the film picturesare adjusted, the

screen is colored the proper shade of yellow to panying drawing inwhich,

Fig.1 is a perspective view; and

Fig. 2 is a sectional view through the aforesaid juxtaposed screenareas.

The particular method chosen for the purpose of illustration involves aprojection screen I, a v

projector 2, an auxiliary screen I, an auxiliary projector 4 and a mask5 for shielding the auxiliary screen 3 from the light of the projector2.

"The screen I and the projector 2 comprise re lar equipment in thetheater where the test is being made, the other apparatus being portablefor convenient removal from theater to theater. The auxiliary screen 3may be supported in juxtaposition to the screen I in any suitable manneras by means of the tripod 6. v 1

The auxiliary projector 4 is preferably moun ed on a cabinet 1containing means for regulating the voltage and current of theprojector, together with metersfor indicating values of potential andcurrent. The mask 5 may be mounted in any suitable way as by means of anadjust-' able post 8 extending upwardly from the cabinet I. Mounted onan extension 9 of the casing of the projector 4 is a filter holder l0into which.

may be dropped one or more filters of diflerent thicknesses and colors.

To determine the proper color of the screen I for use with theparticular color of light emitted by the projector 2, the screen i isilluminated by the projector 2, with the projector operating at thevoltage. supplied to the projector 4 and/or varying the filters in theholder Ill and/or replacing screen 3 with a screen of different color,the tone value of the auxiliary screen can be made substantially tomatch the tone .value of the screen I. Having previously determined thescreen color corresponding to each combination of filters and/or voltagein the auxiliary projector and/or color of auxiliary screen, theaforesaid test indicates the hue which the screen I must be colored tocompensate for the off-color of the light from projector 2, thereby toproduce in the pictures reflected from the screen I a color balancecorresponding to th: aforesaid color balance of the dim picturesnotwithstanding the improper color value of the light from" projector 2.When projecting pictures upon the two screens the pictures should 'bethe same or at least similar in color.

As an example of the foregoing the following procedure may be followed.First select a standard projection system with a screen and projectionlight of known color, preferably one approximating that of the averagetheater. Alongside this system set up one of the aforesaid auxiliarysystems which has a Mazda lamp and precision means for adjusting thecolor temperature of the lamp to a predetermined value (say 3200 K.) orto some indicated departure from I that value. With thecolor temperatureof the Mazda lamp at said predetermined value the color of the auxiliaryscreen is varied by application of difierent pigments until it appearsto match the screen of said standard system. For

example, the pigments may comprise flat white, ultra marine blue andultra marine green and the proportions required to produce the standardauxiliary screen may comprise:

Parts Flat white 90 Ultra marine blue 5 Ultra marine green 5 Theaforesaid color temperature and auxiliary screen color are then adoptedas the standard conditions for use in regulating the color balance ofthe picture in the process of manufacture; that is the pictures areproduced so that, when projected with a Mazda lamp at said colortemperature upon a screen having the same color as said auxiliaryscreen, the pictures present the desired color contrast.

For use in testing the projection conditions in the different theatersin which the pictures are to be projected, different proportions of saidpigments are used to produce a series of auxiliary screens which differin color from said standard auxiliary screen in regular steps, theseries of screens covering the entire range of screen col- Screen No.Subtract 1 part ultra marine blue.

2 parts ultra marine blue. 3 parts ultra marine blue. 1 part ultramarine green. 2 parts ultra marine green.

3 parts ultra marine green. r

Thus, for example, the proportions for 113 and 3G would be as follows:

Flat white 90 4 Ultra marine blue 5 6 Ultra marine green 2 ner butwithout pictures, the standard auxiliary screen is inserted in theauxiliary screen holder and the auxiliary Mazda lamp is operated at theaforesaid predetermined color temperature. If the colors of the twoscreens appear identical then the theater system will display theaforesaid-pictures in proper color balance without altering the theaterconditions. However if the two screens do not match the auxiliary screenis replaced by first one and then another of said series of auxiliaryscreens until the theater screen and auxiliary screen do match. For eachauxiliary screen there is a tint which, when applied to the theaterscreen, will make it match the standard auxiliary screen and thereforedisplay the aforesaid pictures with the desired color balance, theparticular tintx'being determined empirically. For example the aforesaidscreens may indicate the following tints.

Screen No. A volatile solvent containing- 1 part ultra marine blue. 2parts ultra marine blue. 3 parts ultra marine blue. 1 part ultra marinegreen. 2 parts ultra marine green. 3 parts ultra marine green.

Thus if auxiliary screen No. 3B is required to match a theater screenthe latter should be tinted lwlith a carrier containing 3 parts ultramarine Inasmuch as it is the color of the light reflected from thescreens which is to be matched (rather than the color of the screens perse) and inasmuch as the color of the light reflected from a screen maybe variedby changing the color of the light projected to the screen (aswell as by changing the color of the screen) the light reflected fromthe screens may be matched by changing the color of the light projectedupon either screen. Thus instead of interchanging auxiliary screens tomatch the theater screen only the aforesaid standard screen need beused, the matching then being effected by varying the voltage of theauxiliary projector or by inserting different filters in the auxiliarybeam, each voltage and each filter indicating a certain tint to beapplied to the theater screen as determined empirically.

In many cases the difliculty is not with the color of the theater screenbut with the color of the projector light. Obviously the aforesaidmethod indicates the right screen color to display the pictures indesired color balance because the apparent color of the theater screenin matching it with an auxiliary screen, depends upon the color of theprojection light as well as the color of the screen itself. Thus themethod broadly involves any correlation of the color of the lightreflected from the screen with the color of the projection light, byselectively absorbing 2,286,930- from the projection light, uniformlythroughout the cross-sectional area of the projected beam of light,those predetermined color components which tend to make thecolor balanceof the' screen pictures differ from the color balance of the filmpictures. If the color of the light reflected from the two screens ismatched by altering the color of light projected to the picture screenit is preferably done with pre-cali-brated transmission filters inpreference to change in voltage of the projector lamp.

It should be understoodthat the present disclosure is for the purpose ofillustration only and that this invention includes all modifications andequivalents which fall within the scope of the appended claims.

This application is in part a continuation of Y my prior applicationSerial No. 221,557, filed July 27, 1938.

I claim:

l. The method of projecting natural color pictures on a picture screen,the color of the screen or the projection light being unknown, with acolor balance substantially the same as that produced with a standardsystem having an auxiliary screen and auxiliary light of known colors,the method comprising projecting said projection light on said picturescreen without color-picture film in the path of the light, projectingsaid auxiliary light on said auxiliary screen, producing a variation inthe color of the light reflected from one of said screens until itmatches the color of the light reflected from the other screen, saidvariation indicating the color components to be absorbed from the lightin order to make the color of the light reflected from the picturescreen match the color of the auxiliary light reflected from theauxiliary screen, and then projecting the color pictures on the picturescreen with said projection light while absorbing the 40 said colorcomponents from the light uniformly throughout the entirecross-sectional areaof the light. p

2. In the art of projecting color pictures having a predetermined colorbalance, the method of determining the combination of colors of pro-' Ijection light and picture screen respectively which will display saidpictures with the desired combination of colors which is required todis-.

play said pictures with the desired color balance.

3. The method of projecting natural color pictures on a picture screen,the color of the screen or the projection light being unknown, with acolor balance substantially the same as that produced with a standardsystem having an auxiliary screen and auxiliary light of known colors,the method comprisingprojecting said projection light on saidpicturescreen without color-picture fllm in the path of the light, measuringthe color of the light reflected from the picture screen to determinethe color components which make it differ in color from that of theauxiliary light reflected from the auxiliary screen, and then projectingthe color pictures on the picture screen with said projection lightwhile absorbing said color components from the light uniformlythroughout the entire cross-sectional area oi! the light.

' a, F. aacxm'r.

